Identified as Molly B, the woman was arrested during an overnight raid on a house in western Belgium which took place between Tuesday and yesterday, the federal prosecutor's office said in a statement.
"The investigation shows indications of assistance being provided by the woman to persons with the intention to commit an attack in Europe," it said.
She was charged with "participation in the activities of a terrorist organisation."
It said the investigation was completely independent of the probes into the November 2015 attacks in Paris and the March 2016 bombings in Brussels.
Belgium has remained on high alert since March 22 last year when three home-grown suicide bombers attacked Brussels airport and a metro station near EU headquarters, killing 32 people and wounding hundreds more.
The Islamic State group in Syria and Iraq claimed responsibility for the bombings that investigators say were carried out by the same cell that slaughtered 130 people in Paris on November 13, 2015.